In general, a printed circuit board is a flat board whose front contains slots for integrated circuit chips and connections for a variety of electronic components, and whose back is printed with electrically conductive pathways between the components.
A semiconductor apparatus is fabricated by mounting semiconductor integrated circuits onto a printed circuit board. Such a semiconductor apparatus hereinafter is called a "module". In recent years, multi-layered structural type modules have been used to improve integration rate and high-frequency characteristics.
A conventional semiconductor apparatus (module) includes a semiconductor chip; leads connected at one end to the semiconductor chip; metal wires connected between the semiconductor chip and the leads; and a seal material (package). The seal material (package) may be made of epoxy resin or silicon resin to protect the semiconductor chip.
The module also includes a layered printed-circuit-board and pads, formed on the layered printed-circuit-board. The pads are electrically connected to the leads through conductive material paste (conductive adhesive), such as solder or silver paste.
Usually, the package has a thermal expansion coefficient of around 7.times.10.sup.-6 /.degree. C., while the layered printed-circuit-board has a thermal expansion coefficient of around 15.times.10.sup.-6 /.degree.C. It means that there is a lot of difference in thermal expansion coefficient between the package and the layered printed-circuit-board.
In fabrication process of a module (semiconductor device module), a temperature cycling test is carried out. According to such a temperature cycling test, the temperature atmosphere of the module is changed with a predetermined cycle. According to the conventional module, in the temperature cycling test, mechanical stress is concentrated at the conductive material paste, because of the difference of thermal expansion coefficient between the package and the layered printed-circuit-board. As a result, a crack may be made in the conductive material paste. Such a crack results in a disconnection, and therefore the module becomes inoperative.
For solving the above problems in a temperature cycling test, a printed circuit board having a low thermal-expansion-coefficient can be used. If such a printed circuit board is used, the costs for the module is increased.